Expression of human L1 reverse transcriptase in E. coli. (A) Domain structure of human L1 ORF2 protein. The conserved domains are shown as shaded rectangles. L1 RT domain (Aa 238-1061) was cloned into pMal-c2X downstream of MBP gene in frame. (B) Human L1 RT domain was expressed in E. coli as a fusion protein (MBP-RT) and purified as described in materials and methods. The sample was resolved by 4-20% SDS/PAGE with Coomassie blue staining. Protein molecular mass markers are to the right (kDa). The arrow indicates the mobility of MBP-RT fusion protein.